Open University has attracted more than 1m active subscribers to its courses available on Apple's iTunes U app for iPad in less than three months since its launch.

OU says its 52 courses have generated more than 50m downloads globally through the app, and are currently running at more than 40,000 new ones a day.

"With more than 50 million downloads to date, we know that students value our high-quality learning materials, and that is really underlined by the speed with which we have reached one million iTunes U app course subscribers," says vice-chancellor Martin Bean in a statement.

The courses are delivered in Apple's iBook format to the app, with photos, videos and interactive diagrams alongside the course texts.

OU's latest course, Moons: An Introduction, has a "Virtual Microscope" feature for zooming in on and rotating sections of moon rocks.

"We plan to expand our brand new format library with highly interactive iBooks very soon. If you think that a slice of moon rock under a microscope looks fabulous in an iBook, just wait until you see what we can do with Art History," says Bean.

OU's The New Entrepreneurs course has more than 100,000 active subscribers through the iTunes U app, with six more courses having reached the 50,000 milestone.

Apple launched the iTunes U app on 19 January, as the education sector's equivalent of its iBooks app and store. Other course publishers using the platform include Harvard University, TED, MIT and Stanford.

At the time of writing, Moons: An Introduction is the most popular course on iTunes U in the UK, with two more OU courses – What Is Religion? and Introducing Philosophy: Thinking and Ethics in the top 10.